Luis rowed his boat for $5$ kilometers on each of the past $4$ days. How many kilometers did Luis row his boat altogether?
The total number of kilometers rowed is the product of the number of kilometers rowed each day and the number of days that Luis went rowing. The product is $5\text{ kilometers per day} \times 4\text{ days}$ $5\text{ kilometers per day} \times 4\text{ days}= 20\text{ kilometers}$ Luis rowed a total of $20$ kilometers.